The cholinergic system plays an important role in the regulation of the mammalian heart with both chronotropic and ionotropic effects. Acetylcholinesterase (AChE) which metabolizes acetylcholine occurs in multiple stable forms and various tissues have differing amounts or only certain molecular forms. The rodent heart has been shown to have both globular and asymmetric AChE forms. Since AChE plays a role in the regulation of the parasympathetic control of the heart, it seems imperative to have an understanding of the locations and functions of the various AChE molecular forms in the heart. It also seems important to understand what happens to the various forms of AChE in disease, development and aging. In the past only the total AChE activity was investigated in heart disease and development with little regard for the contributions of the specific forms of AChE to the total activity. The present proposal is a first step in answering the question of whether the specific AChE molecular forms have specific functions in mammalian heart by determining if each form has a specific anatomical distribution and also by examining the development of the cardiac AChE molecular forms and correlating their developmental pattern with the anatomical and physiological development of the heart. It is intended that these experiments will provide the ground work for future studies of changes in AChE molecular forms in pathological conditions and in aging.